Journal Article

Neutral hydrogen absorption observations of the central region of NGC 5929

G. H. J. Cole, A. Pedlar, C. G. Mundell, J. F. Gallimore and A. J. Holloway

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 301, issue 3, pages 782-786
Published in print December 1998 | ISSN: 0035-8711
Published online December 1998 | e-ISSN: 1365-2966 | DOI:
Neutral hydrogen absorption observations of the central region of NGC 5929

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We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 1021 cm−2. Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE-SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s−1) and full width at half-maximum (43 ± 6 km s−1) of the absorbing gas with previous [O III] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 1021 cm−2) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.

Keywords: galaxies: active; galaxies: individual: NGC 5929; galaxies: ISM; galaxies: Seyfert; radio lines: galaxies

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Subjects: Astronomy and Astrophysics

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